Various aspects of the biology of the hypothalamic releasing hormone, thyrotropin releasing factor, will be studied. The mechanism of its biosynthesis will be investigated in an invertebrate in vitro model system. The mechanism of TRH release and its regulation by putative neurotransmitter agents will be investigated in vitro using amphibian preoptico-posterior pituitary explants in long term organ culture as a source of TRH-synthesizing neurons. The mechanism by which TRH influences neuronal activity will be studied in invertebrate neurons in vitro using a combined biochemical and electrophysiological approach. Finally, the hypothesis that TRH serves as an osmoregulatory principle in poikilotherms will be tested.